The present invention relates to a variable displacement oil pump used as an oil pressure source for supplying oil to sliding contact portions of an internal combustion engine, for example.
An example of the variable displacement pump is shown in JP 2014-105623A (corresponding to US2014/0219847A1).
To supply the oil discharged from the oil pump to various sections having different required oil pressure levels, such as sliding contact portions of an internal combustion engine and a variable valve actuating device for controlling an operating characteristic of an engine valve, there is a recent demand for a two-step or multistep characteristic having a lower pressure characteristic for a first rotational seed region, and a higher pressure characteristic for a second rotational speed region.
The variable displacement oil pump of the above-mentioned patent document is designed to satisfy such a demand, with first and second control oil chambers formed between a pump housing and a cam ring. By controlling the introduction of the discharge pressure into the first and second control oil chambers with a pilot valve in accordance with an urging force based on the internal pressure in the first control oil chamber, to urge the cam ring in a direction decreasing the eccentricity or eccentricity quantity of the cam ring (concentric direction), an urging force based on the internal pressure in the second control oil chamber, to urge the cam ring in a direction increasing the eccentricity of the cam ring (eccentric direction), and a spring force of a spring to urge the cam ring in the eccentric direction, this variable displacement oil pump controls the eccentricity of the cam ring in a manner of two steps in dependence on the engine speed, and thereby satisfies the different required discharge pressure levels.